1. Field of the Invention
The present invention relates to battery units, particularly a battery unit that allows sensing of a state of charge/discharge of a solid-state battery.
2. Description of the Background Art
Conventionally known batteries include an all solid state type battery, as disclosed in Japanese Patent Laying-Open No. 2004-265685, for example.
Japanese Patent Laying-Open No. 2004-265685 teaches that a raw material including lithium sulfide with a crystal particle size of 140 nm or less is used as a starting raw material in producing lithium ion conductive sulfide glass. The raw material is vitrified by mechanical milling.
Then, the lithium ion conductive sulfide glass is fired at a temperature equal to or higher than the glass transition temperature to produce lithium ion conductive sulfide glass ceramic.
A battery that allows measurement of the remaining capacity of the battery is disclosed in Japanese Patent Laying-Open No. 2005-285647, for example. The battery includes a lithium ion secondary battery, a pressure sensor stacked on the lithium ion secondary battery, and a clamp member clamping the lithium ion secondary battery and pressure sensor from both sides in the stacking direction thereof.
In the event of the lithium ion secondary battery being expanded/shrunk by charging/discharging, the force applied to the pressure sensor is altered accordingly. Change in the volume of the lithium ion secondary battery is detected as the output value from the pressure sensor.
In a state estimation system of a secondary battery disclosed in Japanese Patent Laying-Open No. 2006-12761, each secondary battery cell includes a positive electrode and a negative electrode stored in a casing.
A temperature sensor is disposed between binding plates, affixed integrally with the secondary battery cell. The temperature sensor is arranged to allow sensing of the temperature of the positive electrode and negative electrode for at least one secondary battery cell. An ECU (Electronic Control Unit) provides the state of charge (SOC) of the secondary battery based on the pressure detected value from a pressure sensor and a temperature detected value from the temperature sensor, taking advantage of the volume changing property of the electrode in response to the temperature.
An overvoltage detection device disclosed in Japanese Patent Laying-Open No. 2006-269345 includes a laminate coat battery formed of a lithium ion secondary battery stacked in the thickness direction, and a pressure sensor inserted between the stacked surfaces of adjacent laminate coat batteries in a stacked body of the laminate coat batteries.
Determination is made as to whether overvoltage is generated or not at the laminate coat battery depending upon whether the contact pressure detected by measuring the pressure (contact pressure) acting on the stacking surface exceeds a threshold value or not.
The sodium sulfur secondary battery disclosed in Japanese Patent Laying-Open Nos. 2005-285647 and 2001-176544 includes a solid-state electrolyte with conductivity of sodium ions, a positive-side active material formed of sulfur or sodium polysulfide, stored in a positive-side chamber, a negative-side active material formed of sodium, stored in a negative-side chamber, and means for measuring the amount of molten sodium present in the negative-side vessel. The amount of sodium and change in the fluid level caused by the flow of sodium ions into or out from the positive-side chamber during charging/discharging are measured to obtain the depth of discharging of the battery. Specifically, an electron conduction circuit is formed in the negative-side vessel to identify change in the fluid level by the modification of the electron resistance, and/or measure the pressure change in the negative-side vessel to identify change in the amount of sodium.
The battery disclosed in Japanese Patent Laying-Open No. 2004-265685 is disadvantageous in that press-formability is poor since the lithium ion conductive glass ceramic corresponds to crystallized powder.
The battery disclosed in Japanese Patent Laying-Open No. 2005-285647 includes a negative-side active material and positive-side active material as well as a conduction additive in granular form, exhibiting gaps between the particles. When the battery is expanded or shrunk by the charging or discharging of the battery, the particles of the negative-side active material, the positive-side active material, and the conduction additive of the lithium ion secondary battery are rearranged.
Accordingly, a proper correlative relationship cannot be found between the state of charge and the volume change of the lithium ion secondary battery. The battery of Japanese Patent Laying-Open No. 2004-265685 was disadvantageous in that the state of charge of the lithium ion secondary battery cannot be identified correctly.
Similarly, the state estimation system of a secondary battery disclosed in Japanese Patent Laying-Open No. 2006-12761 and the overvoltage detection device disclosed in Japanese Patent Laying-Open No. 2006-269345 cannot exhibit a proper correlative relationship between the state of charge and the volume of the secondary battery. The remaining capacity in the secondary battery could not be calculated correctly based on the output from the pressure sensor.
The method of measuring the depth of discharge of a battery disclosed in Japanese Patent Laying-Open Nos. 2005-285647 and 2001-176544 is disadvantageous in that it cannot be applied to a solid-state battery.